Influence of Pre-Plasma on Accelerated Protons in Ultraintense Laser Interaction with Not-So-Thin Foils

Abstract

We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a three-fold increase in the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. The foil target is sufficiently thick to prevent disruption of the sheath field at the rear surface by the shock launched by the pre-pulse. Measurements are compared with accurate, numerical hydrodynamic and Particle-In-Cell simulations where the role of the finite plasma scale-length at the laser-target interface is taken into account and the role of stochastic heating in enhancing fast electron production is discussed.

Acceleration of 60 MeV proton beams in the commissioning experiment of SULF-10 PW laser

“…A key parameter for laser–solid interaction at relativistic intensities is the temporal contrast of the laser pulse. Pre-pulses of intensity above 10 10 W/cm 2[ 24 ] would ionize the target, introducing low-density pre-plasmas in front of the target, which could enhance proton acceleration [ 25 , 26 ] . However, if the pre-plasma induced by pre-pulse driven shock appears at the target rear, proton acceleration will be restricted [ 27 ] .…”